Fernandes took his UEFA B diploma through Manchester United alongside Juan Mata and Nemanja MatiΔ, and told the Men in Blazers Media Network that Lacey was in the club's under-14s side at the time.
"His technical ability was never in doubt," Fernandes said. "I often joke with him because I coached him when I was taking my coaching badges, and I remember he was in the U14 team then. So, Juan Mata and I basically coached him for a day.
"I told him he's much better now than he was at 14. He is much more mature, doing very well."
Fernandes went on to describe what he believes separates promising young players from those who make the step up permanently.
"I think what they all need β [if] they want to be part of the team and play for the team β is to treat every training session like a game," he said.
Now 19, Lacey made his United first-team debut against Aston Villa in December and came off the bench in the second half of Saturday's shock 2-0 defeat by Hull. He has been widely tipped for a breakthrough season, and Fernandes believes the teenager has already shown a marked improvement from the player who first emerged last season.
"I think Shea Lacey came with a completely different mentality this season in terms of movement off the ball," Fernandes said.
The United captain, who plays in a similar attacking midfield role to Lacey, said he had taken a close interest in the youngster's early performances this season.
"I think that's great, and it's what I talked to him about after returning from vacation, because I watched their three games. He plays in the same position as me, which requires a high level of running and emotional intelligence in covering space and assisting teammates in attack, and he has done very well," he added.